1. Field of the Invention
The present application relates to the field of biotechnology and, in particular, to the fields of cloning and protein expression.
2. Related Art
The fundamental process that sustains the ongoing biotechnology revolution is the cloning of DNA molecules for their further analysis or use. Cloning of DNA molecules has been practiced in the art for many years. A typical cloning protocol will involve identifying a desired DNA molecule, preparing a population of recombinant vectors by ligating the DNA molecule with a vector in a mixture of DNA molecule, vector and an appropriate ligase enzyme, transforming the population of recombinant vectors into a competent microorganism, growing the microorganism for some period of time sufficient to permit the formation of colonies, selecting colonies of microorganisms that potentially contain the desired DNA molecule correctly ligated in the vector, growing a sufficient quantity of each selected colony from which to isolate the recombinant vector, analyzing the isolated vector to ensure that the vector contains the desired DNA molecule and then growing a sufficient quantity of the microorganism that contains the correct recombinant vector to perform whatever subsequent manipulations are required. For details of various cloning procedures the reader may consult Sambrook, et al. 1989, Molecular Cloning: A Laboratory Manual 2nd Ed. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y., specifically incorporated herein by reference.
The typical cloning protocol outlined above thus includes at least three steps that involve growing of a microorganism. Since these growing steps generally require 12–16 hours and are usually performed as overnight incubations, the rate limiting steps for experiments involving cloning of a DNA fragment are the steps requiring growth of a microorganism. Although there are many variations on the basic practice of cloning, virtually all cloning methods require the insertion of the DNA molecule of interest into a microorganism and growth of the microorganism and, therefore, the speed of virtually every cloning methodology is limited by the rate of growth of the microorganism used for cloning.
For most cloning applications, the microorganism of choice is Escherichia coli (E. coli). Although numerous strains of E. coli are known, most cloning applications use one or another derivative of E. coli K-12. These derivatives suffer from the slow growth rate discussed above. Other known strains of E. coli, such as E. coli W (ATCC9637), have a rapid growth rate when compared to E. coli K-12; however, wild type strains of E. coli W and other rapid growing strains are not suitable for biotechnology applications for several reasons. First, the genetics of the organism have not been determined to the level of detail required by cloning applications. Thus, those skilled in the art would not know whether the genome of a microorganism contained the appropriate modifications of a number of genes that would make the microorganism suitable for biotechnology applications. For example, microorganisms are generally recA+ which leads to the formation plasmid multimers and makes the microorganism less suitable for applications that involve the isolation of plasmid. Microorganisms typically contain numerous protease genes and may degrade overexpressed proteins thereby decreasing the yield of a desired protein product. Microorganisms typically contain a lac operon that does not permit alpha complementation and, therefore, the identification of recombinant vectors is more difficult. Further, many microorganisms contain endogenous plasmids that complicate the plasmid isolation steps necessary for cloning applications. Finally, microorganisms might contain genes coding for nucleases that could cause the degradation of exogenous plasmids.
For a large number of biotechnology applications, a crucial step in the development of the application involves cloning one or more fragments of DNA. Given the central role of cloning in the development of the biotechnology industry, there has long existed in the art a need for reagents that speed the process of cloning. In particular, there exists a need in the art for microorganisms that have a desirable genotype and a rapid growth rate and can be employed to speed the cloning process. The present invention meets this long felt need.